Long Exposures
by William Lulow
We are very used to cameras doing everything for us. If you put your camera on AUTO it will figure out the correct exposure to ensure that you get a good looking image. But, if you have read any of these FREE BLOG ARTICLES, you will know that that’s not the only thing that professional photographers care about. We are used to the ordinary snapshots that are rendered sharp enough and well-lit enough to show people on our cellphones.
There are many good techniques that I have spoken about in some of these articles that can help you turn your plain old snaps into really great images. One of those techniques involves the art of making long exposures. Ordinarily, exposures take place in the hundredths of seconds, fractions of time that are often too short to even notice. But, one of the things you can do to get good exposures is to let more light into the camera by slowing down the shutter speed.
So, here is one scenario: suppose you had a large interior shot to do but could not light the entire area with enough light to provide a good enough exposure that would also have enough detail to show off the space. What would you do?
Suppose you had a scene you wanted to capture but couldn’t find enough light to render it totally visible? There are several things you could do to allow more light into the camera. (1) You could open up the lens’ aperture to its fullest extent. Some lenses have f/1.2 as their largest opening. That aperture allows a lot of light to enter the camera. If that didn’t do the trick, you could (2) increase the ISO (the sensitivity of the camera’s light collecting sensor). Many cameras are capable of ISO settings in excess of 25,000. The thing is, that the higher you set the ISO, the more noise or “grain” you introduce to the image and the less sharp it will be. At some point you will begin to sacrifice detail as the image becomes less and less clear. You can also (3) slow down the shutter speed enough to let more light into the camera so that a proper exposure can be obtained. So, if you intend to use a long shutter speed, you may find that you actually have to cut down on the overall exposure. This sounds kind of complicated, but when you increase the amount of time the shutter stays open, you often have to close down the aperture in order to maintain the correct exposure. Sometimes this can only be done through experimentation. Then you will know how much you need to restrict the aperture to compensate for the long exposure. Sometimes you may need to use filters on your lens to cut down even more on the lens’ aperture.
So, I have a series of neutral density (ND) filters in my camera bag that will cut down the amount of light entering the camera so that I can purposely use a very long shutter speed to get the depth-of-field I want. One of the side effects of long exposures is that anything that keeps moving will not be recorded on the exposure. Note the following example! It should also be said that whenever making long exposures, you absolutely need a tripod and a cable release.
(ND filters come in various densities that will enable photographers to increase exposure times but use smaller apertures):
However, there are times when using one or all three of these techniques still won’t suffice to give you the image you want. What then? Many years ago, I had the task of making images for a catering service that produced many, large parties. The setup of the room was truly amazing, creative and had to be documented. My job was to make images of the party setup and be done before the party started. Many times, the caterer had only a few hours to set up for the party and often wasn’t finished until the guests actually arrived. I however, still had to make acceptable images of the party setup, pack up all my equipment and leave before the first guest arrived. One such party took place in a building’s atrium. The space was so large that it had to be captured from one location. I worked with two assistants and found an ideal spot for the camera as well as positions for a couple of electronic flash units. I knew that if I asked the catering staff to just keep moving while they worked, I could make a kind of “time exposure” in which all those people would disappear if I left the shutter open long enough. I began by making some test exposures to determine the level of light needed to capture the entire interior with just ambient light. I would use a Sekonic incident meter to measure the amounts of light falling on various parts of the scene. I would then adjust my exposure time to render an average image. I would then have to figure out from the combinations of apertures and exposure times, what would yield the best image. Most of the time, I was looking to shoot around f/8 or f/11 in order to provide the optimum amount of depth-of-field. Many of the settings were similar to about 5 minutes @ f/8 with an ISO speed of 100. Sometimes the exposure times were longer. This image was made with about a 15 minute exposure at something like f/11. During the exposure, I had the camera lens open all the time and had my assistants fire the flash units to add density to the images. With a long exposure like this, anyone who kept moving within the scene actually DID NOT REGISTER on the film. Here is one of those images:
As you can tell from the escalators, this was a large space and required a special technique to show all of it in one image. All during this exposure, there were people moving within the scene, but they did not record on the film because of the long exposure and the fact that they kept moving. (There was one person sitting in a chair at the lower left who was folding napkins. He registered slightly on the film but didn’t ruin the shot. Here is another view of this same location:
So the combination of a lot of ambient light plus the addition of “popping” a couple of electronic flash units strategically placed around the venue, made the shot possible. Both of these were approximately 15minute exposures at f/8 or f/11 with an ISO of around 100. So, they were pretty “normal” exposures except for the long exposure times. Here are a few more images which all used the same technique of long exposure times:
In this image, studio flash units were placed strategically to highlight certain areas and the lens was left open to “burn” in ambient light details.
In all these images I had to use a long exposure time in order to render the interiors visible.
Shot in New York City’s “Avery Fisher Hall” back in 1991. Kodak Ektachrome 4×5″ film, ISO 100, f/8 at approximately 3 minutes. You can see how the long exposure is letting light seep in through the windows.
So, to sum up, what a long exposure does is to add enough ambient light so that you can shoot at the aperture you want in order to provide the greatest depth-of-field and/or to make sure everything in the scene registers. Because of the slow exposure, you will need to mount the camera on a sturdy tripod so that it is sure not to move. Then, find out what combinations of ISO and aperture make for the desired result. What happens is that any movement within the scene simply doesn’t register on the film or the sensor. Fast shutter speeds are designed to capture movement and freeze it! When you introduce the concept of movement and so much movement that moving objects or people actually do not get recorded, you often have to MINIMIZE the other parts of the exposure in order to balance the light. Exceedingly long exposure times require you to stop down the lens (use the smallest aperture) as well as use a very low ISO number). A really long exposure to make everything, except movement, register might necessitate using one or more NEUTRAL DENSITY filters over the lens to cut down on even more light than the camera can do by itself.
This really highlights the notion that the more you know about the photographic process, the more creative you can be.
